1. Field of the Invention
The present invention relates to an automatic tool changer for automatically changing tools to be supported on an arm, by pivotally or reciprocally operating the arm.
2. Description of the Related Art
As automatic tool changer, there has been known those disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. Showa 60-31545 and Japanese Unexamined Utility Model Publication No. Showa 61-187641. The automatic tool changer, disclosed in the above-identified publications, has drum-shaped cam for converting rotational input into a swing motion to transmit the swing motion thus converted by the drum-shaped cam to an output shaft for driving the output shaft to rotate at a predetermined timing.
On the other hand, a cam groove is formed on one side surface of the drum-shaped cam for causing a swing motion of a link by the cam groove. The swing motion of the link is then transmitted to the output shaft to cause reciprocal motion of the output shaft in axial direction at a predetermined timing. By rotation of the output shaft, a tool holding arm fixed on the output shaft is pivoted to select the tools. Then, chucking and releasing of the tool is automatically performed by axial motion of the output shaft.
However, in such conventional automatic tool changer, the output shaft is not only rotated but also moved in axial direction. Accordingly, it becomes necessary to certainly provide a space for axial motion of the output shaft within a housing to inherently cause increasing of size of the housing and thus to be a hazard for down-sizing of the automatic tool exchanger.
On the other hand, in the foregoing conventional automatic tool changer, the axial reciprocating motion of the output shaft for chucking and releasing the tool can be obtained by swing motion of the link. The link has a construction to take one end portion as a pivot, the other end portion as a working point and an intermediate portion as a power point engaging with the cam groove. With such link construction, a significant load is created upon transmitting the force. Also, since the output shaft and the tool holding arm are integrally moved in axial direction to create a large inertia force, significant difficulty should be caused in realizing high speed motion of the automatic tool changer.